1. Field of the Invention
The present invention is in the field of material handling systems and specifically relates to apparatus for controlling the rate of discharge of a solid particulate material from a storage hopper.
2. The Prior Art
There has long been a need for apparatus for accurately controlling the discharge rate of particulate materials from a storage hopper. Sometimes the discharge from the outlet of a storage hopper will be used to fill one or more containers, or to provide a continuing flow into a continuous processing unit. At other times, there is a need to control the flow rate at will.
The most common way of controlling the discharge is by the use of a screw, belt or vibrating pan feeder. Sometimes a valve located in the outlet of the storage hopper is used for a crude control. In some instances, a less expensive variable aperture such as a "V" slot ball valve, partially-opened butterfly valve or knife gate is used to modulate the flow.
Several problems are common to the use of aperture-limiting valves. Because the aperture is limited, the material to be discharged may form an arch, bridge or rathole above the limited aperture thereby choking off the flow altogether. Although such flow obstructions may be broken by mechanical means, the resulting intermittent and unpredictable flow is highly undesirable for most applications.
A second major limitation of limited-aperture controllers is that the discharge rate at best cannot exceed the rate produced by gravity flow through the maximum aperture. For such controllers, gravity sets the maximum rate of discharge.
Thus, the more common techniques of controlling the discharge rate are not altogether satisfactory, and the present invention is intended to overcome this problem.